1. Field of the Invention
The present invention relates to an elastic wave device preferably for use in, for example, a resonator or a bandpass filter.
2. Description of the Related Art
Hitherto, elastic wave devices have been widely used as resonators or bandpass filters. Japanese Unexamined Patent Application Publication No. 2011-101350 and WO2011/088904 below disclose a structure of a surface acoustic wave device that suppresses a spurious component in transverse modes by providing a piston mode. For example, in FIG. 9 in Japanese Unexamined Patent Application Publication No. 2011-101350 and in FIG. 4 in WO2011/088904, electrode fingers of an IDT electrode include wide width portions. By providing the wide width portions, a low acoustic velocity region is formed.
In FIG. 12 in Japanese Unexamined Patent Application Publication No. 2011-101350 and in FIGS. 8(c) and 9 in WO2011/088904, a film is laminated on part of the IDT electrode. More specifically, in a direction in which the electrode fingers of the IDT electrode extend, the film is laminated in a region that is located outwardly from a central region. This forms a low acoustic velocity region.
However, in the structure in which the electrode fingers include a wide width portion, there is a limit to how large the width of the wide width portions can be made. That is, when the width is too large, the wide width portions contact adjacent electrode fingers, as a result of which the acoustic velocity in the low acoustic velocity region cannot be made sufficiently low. Therefore, it is difficult to reliably suppress the transverse modes. In addition, a method of laminating an additional layer includes complicated steps, and is costly.